Fabrics may be divided into two general groupings, woven and nonwoven. Woven fabrics may be considered to be any fabric including knitted fabrics in which substantially continuous lengths of fibers, filaments or yarns are connected in a generally regular arrangement or pattern. Woven fabrics are usually characterized by good hand and drape characteristics resulting from mobility of the fiber structure. Also, woven fabrics have good strength and dimensional stability. In contrast, nonwoven fabrics are generally in the form of batt or mat of randomly arranged filaments or fibers, usually of short length, bonded or held together. Nonwoven fabrics are distinguished by a flat sheet-like appearance with a tendency toward boardiness of hand and/or relatively poor strength. The principal advantage of nonwovens is lower cost. This is due to the fact that in the preparation of woven fabrics, it is necessary to spin and twist fibers into yarns; and weave, knit or braid the yarns into fabrics. Because of the lower cost of nonwovens, there has been considerable work to produce a fabric which has a lower cost of nonwoven fabrics while achieving the properties of woven fabrics. The fibers in web form are bonded together, for example, by the application of an adhesive binder or by mechanically compressing the fibers into contact with one another. The binder is selected to give good bonding to a variety of different fibers so that uniform bonding throughout the batt will be achieved.
There are essentially two methods for producing a nonwoven fiber batt, a dry method and a wet method. With the wet method, there is, just as in the production of paper, an emulsion produced which consists of a liquor and fibers which are disposed crossways from which the emulsion and liquor is removed by a force of gravity and by means of suction pumps with subsequent drying units. The wet web producing method features high production speeds and a great uniformity of the web, which consists of crossways lying fibers, but on the other hand it necessitates very power consuming subsequent drying processes and apparatus.
Completely dry processes for forming nonwoven fibrous batts are known and are described in the prior art. The dry method consists of applying a powdery or granular bonding agent or melting film or bonding agents to the web. These bonding agents are then melted with a heating unit and subsequently rehardened so that the web fibers stick together. This method is advantageous because the drying process can be omitted.
The particle size of the copolymer, its method of application to the fibrous web, and the subsequent heating and cooling of the batt all contribute to the strength, resiliency and durability of the batt. The resultant batt, in which fibers are typically bonded to each other at points of contact, possesses properties of lost, light-weight, and resilience which are distinctly superior to those of batts made by other processes.
Some years ago a method was developed for producing a fibrous batt by contacting a thin web of fibers with a bonding agent based on copolymers of vinylidene chloride and vinyl chloride (PVDC-PVC). The process is described in U.S. Pat. Nos. 3,993,518; 4,047,991; 4,050,977; 4,051,294; 4,053,673; and 4,053,674. The PVDC-PVC copolymer has adhesive and melt-flow properties which make it superior to all of the resins known at the time of the referenced invention. The PVDC-PVC copolymer is employed in dry particulate form, thus avoiding the packing and matting which is caused by using polymers in solution, suspension or emulsion form, and at the same time eliminating the cost of removing a solvent or aqueous carrier with heat.
While the PVDC-PVC copolymer has the important advantages cited above, it would be advantageous to provide a copolymer with all the above advantages and the additional advantages of having increased durability to withstand mechanical abuse, particularly during production steps, as well as increased softness for its end-use application.
It is therefore an object of the present invention to provide an improved binding material, which can withstand elevated temperatures for extended periods of time.
A still further object is to provide an improved fibrous batt. Additional objects and advantages of the present invention will be apparent to those skilled in the art by reference to the following detailed description and drawings.